Just bought this game to play on raspberry pi, but it looks like i'm getting error messages that suggest that it's trying to run a 64bit game.. the game folder don't have a 32bit version.

so did they change the game to a 64bit only ?

I don't remember but I think yes, it is 64bit only.

So this is about Warband as mentioned in this thread:
https://www.gog.com/forum/general/mount_blade_warband_did_they_change_it_to_64bit_only

It would be useful to mention which game you are talking about.

It's not going to run because it's a Pi. Raspberry Pis are ARM-based, and modern PC architecture is AMD64 (which is itself a set of 64-bit extensions to the older x86 instruction set architecture).

It's not running because it's the wrong processor architecture, just like how a jailbroken Wii can't have Windows installed onto it because it's PowerPC-based and Microsoft (AFAIK) never released a PowerPC port of any Windows OS. It's also why Apple had to create an emulator to run pre-M1 programs written for OSX, because otherwise no Mac program written before Apple moved to custom ARM chips for their desktop computers would run on the new ARM-based Macs.